The analysis of fluid samples is widely used in the chemical and bioengineering fields as well as in the medical field to clinically diagnose diseases using blood and humoral liquids from patients. For more convenient and efficient analysis of fluid samples, various small diagnostic devices have been developed and utilized. Particularly, a lab-on-a-chip is a device that integrates various laboratory functions such as separation, filtration, mixing, labeling, analyzing, washing, etc., on a small single chip.
While passing through microchannels formed on a chip, fluid samples are allowed to undergo the laboratory mechanisms and are finally detected by means of, for example, a fluorescent label indicating a reaction with an antibody immobilized onto the chip. Thus, it is one of the most important technical factors in quickly obtaining accurate analysis results by use of such miniaturized chips to control the motion of fluid samples through the microchannels formed on the chips.
A driving force to move fluid through the microchannels on a chip may be generated by a small motor or may resort to capillary phenomena. In the case of a chip using capillary phenomenon as a main driving force, the fluid flowing through the microchannels shows irregular and non-uniform mobility patterns, particularly when the microchannels are of extremely low height or are narrowed. These irregular and non-uniform mobility patterns are generated due to the differences in fluid interaction with upper and lower walls and with left and right walls and act as a great hindrance to detecting and analyzing a target contained in a trace amount in the fluid sample.
Also, when closed channels of tens of micrometers in size are formed, it is not easy to uniformly process edge portions of channels without loss, thus causing problems in dimension and quality upon mass-scale production. This minute difference in channel structure disturbs fluid flow, leading to an inconsistent analysis result.
To overcome such problems, Korean Patent Application No. 10-2007-0073659, filed on Jul. 23, 2007, suggests a chip in which one of a pair of inner sidewalls of a channel is adjacent to an extension portion which is more deeply depressed than the channel, so that fluid passes through the channel, with interaction with only the other inner sidewall.
Korean Patent Application No. 10-2007-0073657, filed on Jul. 23, 2007, suggests the effective removal of noise only through microchannel structures and without the use of paper filters or porous membranes, thus quickly performing both quantitative and qualitative analyses with a trace amount of fluid sample.
However, when wall-free, microfluidic chips associated with the above-mentioned techniques are employed, it is necessary to appropriately control the flow of fluid at each step.
For example, as suggested in Korean Patent Application No. 10-2007-0073657, when a fluid sample is fed through a sample inlet into a reservoir, it moves into the microchannels because of fluid pressure and capillary phenomenon, with the concomitant noise filtering of the sample, e.g., blood. In contrast, when fluid is directly introduced into a microchannel of a size on the micro scale, the fluid filling the reservoir has a pressure sufficiently large to spread over the extension portion. Thus, it impedes the wall-free effect suggested by Korean Patent Application No. 10-2007-0073659, resulting in the bringing of errors into the analysis results.
A reaction portion is generally designed to be a site where a label, such as a fluorescent material, is bound to a target and the labeled target undergoes a specific reaction such as an antigen-antibody reaction, so as to activate the label. For accurate qualitative and quantitative analyses, the sample must reside in the reaction portion long enough to sufficiently react with, for example, an antibody.
Therefore, unless the flow of the fluid across the reaction portion is controllably delayed during passage therethrough, an error may occur in the qualitative and quantitative analyses of a target within the fluid. That is, it is necessary to slow the flow rate of the fluid across the reaction portion. At this time, the reaction efficiency may be further increased if reaction samples are mixed.
Leading to the present invention, intensive and thorough research into a microfluidic wall-free chip, conducted by the present inventor, resulted in successfully preventing a sample from leaking into the extension portion upon the introduction thereof into the microchannel and in delaying the flow rate of the fluid enough so that it could sufficiently react therein with the concomitant mixing of reaction samples.